I think that the default overload of == for valarray is not very convenient. By default x==y (for two valarrays x and y) returns a valarray<bool>, with true on the ith entry if x[i]==y[i]. Rather, I need a single bool, which tells me if both valarray<double> contain the same elements or not. I know I can do this with a cycle, but having to do the cycle every time is not convenient. What's the best workaround here? Is there a way for me to define my own overload of == (and also !=, <, and so on)?

C++ fstream is writing hex instead of string?

I'm trying to download a file using URLDownloadToFile() which is working so far, however I'm having trouble with the callback function and writing the callback output wszStatusText to a file.

Here is the function that's giving the problem:

HRESULT DownloadStatus::OnProgress(ULONG ulProgress, ULONG ulProgressMax, ULONG ulStatusCode, LPCWSTR wszStatusText)
{
    fstream myfile;
    myfile.open("file.txt", ios::app);

    // this prints hex e.g. StatusText: 00435F78
    myfile << " StatusText: " << wszStatusText;
    myfile.close();

    // this prints the string properly e.g. text/plain
    MessageBox(NULL, wszStatusText, L"test", MB_OK);

    return S_OK;
}

The thing is that MessageBox() is showing the data properly...

How to declare unique_ptr of vector?

I am trying to declare a global vector of MyClass using unique_ptr. My compiler is 4.8.4.

glo.h

extern std::unique_ptr<std::vector<MyClass>> gl_vec;

glo.cpp

std::unique_ptr<std::vector<MyClass>> gl_vec;

And in the file where I initialize and use it for the first time in a different *.cpp file:

#include "glo.h"

// within function 
{
    gl_vec = std::unique_ptr<std::vector<MyClass>> ();

    cout << "gl_vec size = " << (*gl_vec).size() << endl; // crashes here
}

Things keep crashing when I use the pointer. Anyone see what I'm doing wrong?

Qt QDir::current()

I had some code like this:

void MainWindow::saveData()
{
QDir oldDir=QDir::current();//this should return the main executable directory.Since there is no other place in my hole code where i temper with QDir.
QDir sess("Sessions");
if(!oldDir.exists("Sessions"))//if "Sessions" Dir doesn't exist 
     oldDir.mkdir("Sessions");//create it.
QDir::setCurrent(sess.absolutePath());
//some virtual code inside current Dir, which i didn't implement yet.
QDir::setCurrent(oldDir.absolutePath());//restore old dir
}

When i run my app firstly the code works perfectly.but in the second run, the first call to "QDir::current();" returns the "Sessions" Dir and not the main executable Dir as it should be restored in the first run.actually i did manage to overcome this by adding one line at the biginning of the code, the following :

QDir::setCurrent(QCoreApplication::applicationDirPath());

Still i want to know why the first code didn't work.already checked for the documentation of the functions and found nothing.

gmtime_r((time_t*)&title->start_time, &start_time);

I'm trying to compile on Microsoft visual studio 2013 on C++ a program written for linux ( is a mix of C and C++ (#include .h) and I'm going to convert all in C++ to not be more confused !)

the statement:

gmtime_r((time_t*)&title->start_time, &start_time);

return errors: Error 11 error C3861: 'gmtime_r': identifier not found IntelliSense: identifier "gmtime_r" is undefined

please help

Passing a reference-to-function as a universal reference

I'm struggling to understand what exactly happens when passing a reference-to-function to a function as a universal reference (what type is being deduced). Let's suppose we have a function foo that takes a param as a universal reference:

template<typename T>
void foo(T&& param)
{
    std::cout << __PRETTY_FUNCTION__ << std::endl;
}

And then let's do the following:

void(&f)(int) = someFunction;
foo(f);

The result will be:

void foo(T&&) [with T = void (&)int]

This is perfectly understandable: we are passing lvalue to our function foo, so the deduced type is void(&)int, and the type of the param will be "void(&& &)int" which under reference collapsing rules becomes void(&)int. Param will be just an lvalue reference to a function.

But when I do the following:

void(&f)(int) = someFunction;
foo(std::move(f));

foo will print:

void foo(T&&) [with T = void (&)int]

which is exactly the same as before! What is happening here? Why the result is the same as when passing lvalue? I would expect that since we are passing rvalue to foo, the deduced type should be T = void(int), and param should become void(&&)int. This always happen with all other "normal" types (like classes, primitive types, etc.) Why is it different when dealing with function references?

Refresh a Combobox in C++?

I have a function that detects camera ports in 3D slicer, however it seems to only run once. When I unplug/plug in a camera, the number of ports should update in a combobox (designed in Qt), but nothing changes.

The function I'm using detects when the camera port is clicked:

void qSlicerTrackingModuleWidget::onCameraPortClicked(){
  Q_D(qSlicerTrackingModuleWidget);

  // Clear current entries
  d->CameraPortComboBox->clear();

  int n = 0;

  // Loop over camera ports until last one is found. Add all available ports to combo box and exit.
  while(1){ 
    cv::VideoCapture cap = cv::VideoCapture(n);


    if(!cap.isOpened()){ 
      return;
    }
    QString portNum = QString::fromStdString(std::to_string(n++));
    d->CameraPortComboBox->addItem(portNum);
    qSlicerCoreApplication::processEvents();
  }
}

The setup function runs last and assigns the GUI to the actual function.

connect( d->CameraPortComboBox,   SIGNAL(clicked()),  this, SLOT(onCameraPortClicked()));

I need it to refresh and try to detect the cameras every time the combobox is clicked on, but because of the interface setup I am not sure if it is possible. I don't think constantly refreshing the program is a good option, so I'm out of ideas. Is there any way to do this?